Nontypeable Haemophilus influenzae (NTHi) is a common pathogen that causes otitis media (OM) in children and lower respiratory tract infections in adults, especially those with chronic obstructive pulmonary diseases (Klein et al. 1992 Adv Pediatr 39:127; Murphy and Apicella. 1987 Rev Infect Dis 9:1; Musher et al. 1983 Ann Intern Med 99:344). Prevention of NTHi infections is important because OM is a major cause of conductive hearing impairment in children who are at the critical age for speech and language development (Giebink 1989 Pediatr Infect Dis J 8:S18). The exacerbation of chronic obstructive pulmonary diseases in elderly is life threatening, the fourth leading cause of death in the United States. In addition, repeated or inappropriate antibiotic treatment of OM and other respiratory diseases contributes to the emergence of antibiotic-resistant strains (Berman 1995 N Engl J Med 332:1560). Therefore, there is an urgent need to develop prophylactic vaccines to prevent these NTHi-caused diseases.
In the past years, significant progresses have been made toward identifying vaccine candidates based on NTHi surface antigens such as outer membrane proteins and lipooligosaccharide (LOS). These antigens are potential targets for humoral immunity and bactericidal antibodies that appear to be important in protecting against NTHi OM (Geibink et al. 2002 Ann Otol Rhinol Laryngol 111:S188: 82). Our strategy is to use LOS as a vaccine component, since NTHi does not have a detectable capsular polysaccharide and its LOS is both a virulence factor (DeMaria et al. 1997 Infect Immun 65:4431; Flesher and Insel 1978 J Infect Dis 138:719; Gu et al. 1995 Infect Immun 63:4115) and a potential protective surface antigen (Barenkamp and Border 1990 Pediatric Infect Dis J 9:333; Ueyama et al. 1999 Clin Diagn Lab Immunol 6:96; McGehee et al. 1989 Am J Respir Cell Mol Biol 1:201). Previously, we chemically conjugated a relatively conserved detoxified LOS to proteins to form vaccines (Gu et al. 1996 Infect Immun 64:4047). These conjugates were immunogenic in mice and rabbits and conferred T cell-dependent immunological protection against experimental OM in chinchillas (Gu et al. 1997 Infect Immun 65:4488; Sun et al. 2000. Vaccine 18:1264).
The LOS can also be converted into a nontoxic T cell-dependent antigen through the use of anti-idiotype antibodies (Schreiber 1993 Springer Semin Immunopathol 15:235; Gulati et al. 1996 J Infect Dis 174:1238) or peptides that mimic the LOS (Phalipon et al. 1997 Eur J Immunol 27:2620; Charalambous and Feavers. 1998 Abstracts of the Eleventh International Pathogenic Neisseria Conference. Eds: Nassif et al. p.186. Editions E.D.K., Paris, France.). A strategy based on the mimicry of saccharide antigens by anti-idiotype antibodies is difficult and time-consuming. Recently, phage-display has been used to identify ligands for a variety of target molecules by an affinity selection process called biopanning (Goodson et al. 1994 PNAS USA 91:7129; Szardenings et al. 1997 J Biol Chem 272:27943; Iniguez et al. 1998 J Virol Methods 73:175; Hogrefe et al. 1993 Gene 128:119; Scott and Smith 1990 Science 249:386; Lowman et al. 1991 Biochemistry 30:10832; Smith 1991 Curr Opin Biotechnol 2:668). Random peptide libraries displayed on bacteriophage outer proteins have been used successfully to screen for peptides that bind antibodies as well as non-antibody molecules (Pincus et al. 1998 J Immunol 160:293; Valadon et al. 1996 J Mol Biol 261:11; Moe et al. 1999 FEMS Immunol Med Microbiol 26:209; Grothaus et al. 2000 Vaccine 18:1253; Lesinski et al. 2001 Vaccine 19:1717; Zhang et al. 1997 Infect Immun 65:1158; Yip and Ward 1999 Comb Chem High Throughput Screen 2:125; Hufton et al. 1999 J Immunol Method 231:39; Gardsvoll et al. 1998 FEBS Lett 431:170; Vest Hansen et al. 2001 Eur J Immunol 31:32; Odermatt et al. 2001 J Am Soc Nephrol 12:308). These studies allow investigators to map the target sequences for monoclonal or polyclonal antibodies that recognize both linear and conformational epitopes.
Libraries have been used to identify peptides that mimic the carbohydrate structures of bacteria, cancer cells, or viruses (Pincus et al. 1998 J Immunol 160:293; Valadon et al. 1996 J Mol Biol 261:11; Moe et al. 1999 FEMS Immunol Med Microbiol 26:209; Grothaus et al. 2000 Vaccine 18:1253; Oldenburg et al. 1992 PNAS USA 89:5393; Scott et al. 1992 PNAS USA 89:5398; Zhu et al. 2001 Biochem Biophys Res Commun 282:921; Oleksiewicz et al. 2001 J Virol 75:3277). In the case of bacteria, several studies have reported success in isolating peptide mimetics that elicit an immune response against native bacterial saccharide structures in animal models. A study by Phalipon et al. (1997 Eur J Immunol 27:2620) was an early example of immunogenic mimicry of bacterial saccharides by phage-displayed peptides. They used two monoclonal antibodies specific for the O-antigen part of Shigella flexneri serotype 5a LPS to screen two phage-display nonapeptide libraries. Some of the selected phage clones could induce specific anti-O-antigen antibodies in mice. The immune response selectively recognized the corresponding bacterial strains. Using a similar method, Pincus et al. (1998 J Immunol 160:293) located peptides that bind to monoclonal antibodies specific for type 3 capsular polysaccharide of group B streptococci (GBS). The latter peptide specifically blocked the binding of anti-GBS antibodies to GBS and elicited an anti-GBS antibody response in mice when conjugated to protein carriers. Instead of using peptides from phage display library, Westerink et al. (1995 PNAS USA 92:4021) developed a peptide derived from anti-idiotype monoclonal antibody. The latter peptide elicited a protective antibody of meningococcal group C polysaccharide. Table I summarizes reports of peptide mimetics of bacterial or fungal carbohydrate structures. These studies reveal that some of the mimic peptides only show antigenicity in vitro while others can be antigenic and immunogenic in vivo, indicating a new strategy for selection of immunogens for the development of anti-saccharide vaccines.
TABLE IPeptide mimetics of bacterial (fungal) capsular polysaccharide(CPS), lipopolysaccharide (LPS) or lipooligosaccharides (LOS)MimeticCarbohydratePeptideFeaturesReferenceBrucella LPS6–16merElicits weak anti-De Bolle et al. 1999LOS antibodyJ Mol Biol 294: 181Candida albicans7merElicits anti-β-1,2-Jouault et al. 2001β-1,2-mannosidesmannoside antibodyGlyco-biology 11: 693CPSCryptococcal6, 10merPeptides are goodValadon et al. 1996glucuronoxylomannanantigenic mimetics butJ Mol Biol 261: 11;CPSpoor immunogenic mimeticsValadon et al. 1998Peptides protect againstJ Immunol 161: 1829challengeZhang et al. 1997 InfectImmun 65: 1158Fleuridor et al., 2001J Immunol 166: 1087Group A6, 15merMab binding to peptideHarris et al. 1997 PNASstreptococcal CPSmimetics different thanUSA 94: 2454binding to CPSGroup B12merElicits anti-CPSPincus et al. 1998streptococcalantibodyJ Immunol 160: 293Type III CPSMeningococcal15merElicits anti-CPSGrothaus et al.,group A CPSantibody2000 Vaccine 18: 1253Meningococcal6, 8merPeptides are goodMoe et al. 1999 FEMSgroup B CPSantigenic mimetics butImmunol Medpoor immunogenicMicrobiol 26: 209mimeticsMeningococcalV regionsElicits protective anti-Westerink et al.group C CPSof mAbCPS antibody peptide1995 PNAS USAderived from anti-Id Mab92: 4021Meningococcal7merElicits weak to mediumCharalambous &FeaversLOSanti-LOS antibody2000 FEMS Microbiol Lett191: 45Pneumococcal15merElicits anti-CPSLesinski et al.Serotype 4 CPSantibody2001 Vaccine 19: 1717Shigella flexneri9merTwo of 19 peptidesPhalipon et al. 1997serotype 5a LPSidentified elicitEur J Immunol 27: 2620anti-LOS antibodies